Evaluating treatment outcomes across four substance use treatment settings: a 12-month longitudinal study in Iran

Abstract Background: Substance use disorder is a persistent public-health challenge in Iran, where multiple treatment settings operate in parallel. This study assessed within-modality changes over 12 months among clients in Methadone Maintenance Treatment (MMT), Drop-in Centers (DICs), Therapeutic Communities (TCs), compulsory (Article 16) treatment. Methods: A prospective, naturalistic cohort was conducted across 15 routine-care centers in Kerman Province (May 2023–May 2024). Of 493 enrolled, 470 completed follow-up (MMT/DIC at 12 months; TC/compulsory at end-of-treatment [EOT]). MMT/DIC were assessed at baseline,